Although rare-earth magnesium (Mg-RE) alloys are widely used in various industries, they show much poorer machinability for shaping into desired dimensions than conventional magnesium ones. The most critical issues associated with cutting Mg-RE alloys are high risk of chip ignition and short tool life dominating the chip removal process. The present paper aims to address the tool performances on the machinability of Mg-RE alloys under dry cutting. Four types of tools covering uncoated and diamond-coated ones were examined, and a special focus was devoted to explore the effects of various tool parameters on the milling responses of Mg-RE alloys as well as the underlying wear mechanisms. The experiments reveal that the cutting tools with larger rake, clearance, and helix angles can achieve high-quality milling of Mg-RE alloys at controllable cutting temperatures. The cutting parameters can be maintained at a certain level, such as the cutting speed of 120–240 m/min and the feed per tooth of 0.1–0.2 mm/z, to meet the requirements of safe milling of Mg-RE alloys without ignition risk.

Zirconia ceramics have been extensively applied in dental restoration due to their superior properties and excellent functionalities. Green-compact sintering and mechanical processing have become critical operations to shape these denture materials to target dimensions and desired quality. Improper sintering regulations and cutting-induced damages are crucial issues when dealing with the manufacturing of ceramic dentures as they adversely affect the performance and acceptance of eventually-machined denture products. In this paper, a critical review has been conducted to offer a scientific understanding of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) processing, focusing on illustrating the characteristics and properties of the materials as well as the influence of the sintering process on the microstructure and machinability of the workpiece. Recent advances addressing the processing issues of zirconia ceramics for dental applications are carefully reviewed by critically analyzing the scientific findings reported in the open literature. The fundamental influences of the working conditions on the machining quality of ceramic materials are discussed. The features of emerging non-traditional machining technologies are compared and analyzed. Dentures manufacturers will benefit from this review article as they seek to achieve high-quality processing for zirconia ceramics.

为深入研究氧化锆陶瓷切削加工质量的影响因素并揭示其切削去除机理,开展基于光滑质点流体动力学(SPH)方法的氧化锆陶瓷正交切削仿真研究,模拟材料去除时的大变形行为,揭示了裂纹发展和切屑形成过程.结果表明:脆延转变取决于切削深度,临界转变深度为0.75～1.00μm,其裂纹形式存在明显差异;切屑形态主要分为不连续带状和崩脆粉末状,延性去除时材料变形量与切削深度和切削速度正相关,脆性去除时稳定于极大值;切削力与切削深度正相关,但仅在延性去除时与切削速度正相关,脆性去除时切削力的时序分布与裂纹的发展密切相关.

The 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) is regarded as a superior bioceramic being extensively used in modern denture restoration. However, the material possesses extremely poor machinability and are prone to serious cracking and failure formation due to its exceptionally high hardness and inherent brittleness. Hard milling is a feasible strategy to shape fully-sintered 3Y-TZP to desired quality and target dimensions. The present paper aims to study the milling behaviors and mechanisms of 3Y-TZP ceramics by using superhard PCD and PCBN tools. The fundamental milling responses, including cutting forces, temperatures, and surface morphologies, were all examined. The parametric effects on the 3Y-TZP machinability outputs were addressed. A particular focus is placed on comparing the cutting performances of different tools in milling 3Y-TZP. It is found that the PCD tool outperforms the PCBN tool from the perspective of reducing cutting forces, specific cutting energy consumption, and milling temperatures. To get smooth surface morphologies with minimal damage, the spindle speed lower than 5000 rpm and the feed per tooth lower than 9 mu m/z should be adopted for the PCD tools. However, under large milling parameters, the PCBN tools show advantages in ensuring the stability of machined surface quality for 3Y-TZP ceramics over the PCD ones.

GW63K rare-earth magnesium (Mg-RE) alloys have been widely used in various advanced industries for their excellent mechanical properties. However, the machinability of GW63K alloys under clean cutting conditions still needs to be better understood. The novelty of this paper lies in addressing the influences of varying cutting parameters on the milling responses of GW63K Mg-RE alloys as well as the underlying mechanisms. A full-factorial design of experiments was conducted under dry cutting and minimum quantity lubrication (MQL) conditions. A three-tooth milling cutter with a diameter of 12 mm was used during the investigation. The critical milling outputs involving cutting forces, machining temperatures, and surface quality attributes were carefully analyzed. The results indicate that the cutting force highly depends on the feed per tooth, and the cutting temperature is raised with the increased cutting speed and feed per tooth. The MQL is found capable of reducing the milling temperature by 10.8 degrees C on average compared with dry cutting. The MQL shows benefits in improving the cutting performances of tools and surface quality of Mg-RE alloys by reducing the tool-workpiece friction coefficient and enhancing the heat dissipation conditions of the chip contact surface. In addition, lower feed per tooth and higher cutting speeds under MQL conditions are suggested for the milling of Mg-RE alloys while ensuring processing efficiency.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The 3 mol% yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics have been extensively used in restorative dentistry due to their excellent esthetic effects, good chemical stability, and superior biocompatibility. Mechanical milling and surface texturing are two important aspects when dealing with the processing of zirconia ceramics for dental applications. The present paper reviews the recent advances achieved in the mentioned research fields. The fundamental milling features of 3Y-TZP ceramics are initially introduced with a particular focus on the cut surface quality. The effects of different process parameters on the machinability of 3Y-TZP ceramics are briefly summarized. Additionally, the basic mechanisms of surface texturing of these bioceramics are introduced. The mechanisms controlling how the microtextures affect the service performances of 3Y-TZP are carefully reviewed. Finally, the current research challenges and the future perspectives concerning the mechanical processing of 3Y-TZP are outlined.

Aluminum alloys have been extensively used in aerospace, machinery, transportation, and other industries due to their superior strength, relatively low weight, and outstanding thermal conductivity. High-speed cutting (HSC) and minimum quantity lubrication (MQL) techniques have been widely applied for the machining of aluminum alloys. This paper investigates numerically the influences of various geometrical tools on the cutting behaviors, in particular, the cutting forces/temperature of aluminum alloys. The effects of the rake angle and the friction coefficient are examined by simulations based on the orthogonal cutting mode. The findings of the numerical analysis may guide the design of cutting tools in high-speed MQL cutting for aluminum alloys.

A series of milling experiments are carried out on GW63K magnesium alloys under the dry and MQL cooling conditions.The effects of different milling parameters and cooling conditions on the cutting forces and temperatures of GW63K alloys are analyzed, and the machined surface quality and morphologies are studied.The results show that higher cutting speed and feed per tooth lead to a higher resultant milling force under both cooling conditions, and the impact of the feed per tooth becomes more significant.The resultant milling forces are also higher under the MQL condition compared with the dry cutting.The milling temperature also increases with larger cutting speed and feed per tooth.In the dry milling, higher milling temperatures are obtained.The feed per tooth has a significant effect on the machined surface quality of GW63K magnesium alloys, while the MQL reduces the machined surface roughness and improves the surface quality.In conclusion, the miling properties of GW63K magnesium alloys can be improved with the use of MQL and the selection of lower feed per tooth and higher cutting speed.

One of the most important and often employed indicators for describing machinability and machining quality is tool wear. While flank wear is commonly used to gauge the extent of a worn scar, tool wear is characterized more by its shape than its size. To quantify the wear shape, more specific data concerning the wear contour is required. With this aim, the present work addresses the fundamental wear mechanisms and failure modes of several coated tools used in the mechanical milling of rare-earth magnesium (Mg-RE) alloys. Uncoated, edge-strengthened, TiAlN-coated, and diamond-coated tools were tested under dry and minimal quantity lubrication (MQL) conditions. The cutting energy flow and consumption rules governing the tool wear processes were quantified using the exergy analysis theory. The results indicate that the cutting performances of tools and the surface quality are both enhanced by the MQL through reducing adhesion wear. For the unstrengthened tool, a tool wear reduction of 55% is achieved by the MQL. While for the TiAlN-coated tool, the tool wear can be furtherly suppressed by 49%.

Zirconia ceramics have emerged as a promising restorative material owing to their superior physical properties and excellent biocompatibility. Among the zirconia family, fully-sintered samples show the highest mechanical properties but the poorest machinability compared with those fabricated at pre-sintering temperatures. The current work aims to study the milling characteristics of fully-sintered zirconia ceramics when using polycrystalline diamond (PCD) tools under varying cutting conditions. The machining responses of fully-sintered zirconia ceramics, such as cutting forces, specific cutting energy, milling temperatures, and surface topographies, were carefully addressed. The obtained results were correlated with the applied milling parameters. The tool wear morphologies were eventually characterized to figure out the underlying wear mechanisms governing the performance of PCD tools. The results indicate that increasing the feed per tooth definitely raises the milling forces and temperatures, while increasing the cutting speed elevates the milling temperatures but decreases the cutting forces. The feed per tooth significantly affects the surface topographies of cut zirconia surfaces due to its effects on the ductile-brittle transition of the workpiece. The PCD tool shows the feasibility of carrying out hard milling of fully-sintered zirconia ceramics, which undergoes a minor degree of wear along its cutting edge.

High-strength carbon fiber reinforced polymers (CFRPs) are advanced superhard engineering materials being extensively utilized in modern aerospace industries but show poor machinability. The present paper aims to address the performance of the diamond-coated special tools on the machining properties of high-strength CFRP composites. The studied CFRP specimen was a multidirectional composite laminate fabricated by high-strength T700 carbon fibers and epoxy resin. The tool performance on the cutting of high-strength CFRPs was studied in terms of thrust force, specific drilling energy, surface defects status, and cut product quality. The results indicate that tool geometries significantly affect the composite cutting responses, and the step drill outperforms the candlestick tool due to the step-shaped structure that alleviates the severe interaction with the hard CFRP composite workpiece during the chip separation process. The CFRP composite is prone to serious surface flaws because of its inherent anisotropy and heterogeneity despite the use of diamond-coated tools. Moreover, well-designed geometrical modification of diamond tools can greatly improve the composite surface quality.

Polycrystalline diamond (PCD) is a superhard tool material capable of resisting harsh tool-work interactions when machining hard workpiece materials due to its superior thermo-mechanical properties. Zirconia ceramic represents one type of biomedical-grade restorative material being extensively utilized in clinical dental prosthodontics owing to its outstanding biocompatibility and excellent esthetical effects. The present paper aims to carry out a series of milling experiments against the zirconia ceramics when using the PCD tools. The main objective of this work lies in evaluating the wear behavior of PCD tools following the milling of zirconia ceramics. Two types of zirconia specimens, including the pre-sintered and fully-sintered 3Y-TZP ceramics, were examined. The tool performance was assessed in terms of the wear development, and the worn tool surface morphologies were characterized using both the digital microscope and the surface topography measuring instrument. Moreover, the underlying mechanisms governing the wear progression of PCD tools were revealed with respect to different sintered ceramic specimens.

Sintering is a comprehensive process that involves the complex evolution of material microstructures and properties, being recognized as a critical factor to improve the machinability of ceramics. The present work aims to address the evolution of the material removal mechanisms of the 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) during the sintering process based on the micro scratching tests. The impacts of sintering temperatures on the material removal behaviors, including scratching forces, scratch morphologies, specific scratching energies, and critical transition depths, were rigorously studied. The acquired results indicate that the intergranular bonding strength is a critical factor that determinines the material removal mechanisms of 3Y-TZP, and 1100 °C signifies the transition threshold for the material removal mode. After 1100 °C, the material removal mechanism has gradually converted into the typical ductile-brittle removal regime. Moreover, the critical depth in ductile regime at 1200 °C is about 1.89 times that at 1500 °C, and the critical depth of ductile-brittle transition at 1200 °C is approximately 2.08 times that at 1500 °C.

Electrostatic minimum quantity lubrication (EMQL) is a newly-developed cooling method dedicated to crucial manufacturing processes; however, its applicability under the high-speed machining (HSM) of aluminum alloys remains poorly understood. In this paper, parametric tests under the EMQL condition and their comparisons with the dry, flood cooling, and conventional MQL conditions were conducted during the HSM of AlSi7Mg alloys. The specific energy consumption, machined surface morphologies, and wear signatures at the tool edge were experimentally investigated. Based on the results obtained, the machinability of AlSi7Mg under EMQL is characterized, and the feasibility of EMQL is addressed. The EMQL generally shows better lubricating and cooling effects in the HSM of AlSi7Mg alloys, in which the best-machined surface quality and the least tool wear and adhesion are achieved. The cutting depth is noted as the most influential factor affecting the machined surface roughness under the EMQL conditions. The compatibility of the EMQL with the HSM of AlSi7Mg alloys is confirmed in this study, and technical guidance for selecting cutting parameters is offered for the manufacturing community.

Fully-sintered 3 mol % yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics have been recognized as a promising restorative material for dental applications because of their unique properties and superior biocompatibility. Hard milling using polycrystalline diamond (PCD) tools is a feasible strategy to shape the extremely hard ceramics into desired quality and target dimensions. The present paper aims to address the wear behaviors and mechanisms of PCD tools following the hard milling of 3Y-TZP ceramics. The workpiece specimens were prepared at the fully sintering temperature to completely porcelainize the zirconia substrate, and the PCD straight edge was brazed onto the tungsten carbide tool body along the tool axis direction to ensure the successful orthogonal milling of the workpiece specimen. A series of hard milling experiments were conducted by changing the spindle speed on a five-axis CNC machining center. The wear morphologies of worn PCD edges were examined using the scanning electron microscope (SEM) to identify the dominant wear modes and failure patterns governing the hard milling of 3Y-TZP ceramics. The effect of the spindle speed on the tool wear patterns was studied. The obtained results provide several technical guidance for the hard milling of fully-sintered 3Y-TZP ceramics.

Composite/titanium stacks are extremely difficult to machine due to the generation of severe interface damage, being the critical defect to suppress. The present paper aims to use the finite element method (FEM) to investigate the interface damage formation mechanisms following the machining of CFRP/Ti6Al4V stacks with a particular focus on the distribution of stresses and temperatures. Its key objective lies in revealing the effects of different cutting sequence strategies on the interface damage formation to guide the design of the stack machining pro-cesses as well as the selection of cutting sequences. A micro-mechanical orthogonal cutting model and a 3D drilling model of the CFRP/Ti6Al4V stacks were developed to explore the fundamental cutting edge/material interactions and the damage formation mechanisms under both the CFRP-* Ti and Ti-* CFRP strategies. The investigations confirm the dominant impact of the cutting sequence strategy on the stress and temperature distribution during the machining of CFRP/Ti stacks, which is mainly responsible for the diverse interface damage. Besides, the interface damage of a material layer becomes more serious when the material is machined as a secondary phase due to the adhesion and abrasion of previous material chips. The coupling effects of the matrix damage and the interface bending are the influential factors leading to severe interface damage under the Ti-* CFRP strategy, thereby unfavorable for the interface quality.

Carbon fiber reinforced polymers (CFRPs) have been extensively used in diverse industrial fields owing to their superior properties and excellent functions. Mechanical drilling has become a compulsory operation to shape these composites to target dimensions and desired quality for assembly purposes. Cutting-induced damages are critical issues when dealing with the manufacturing of CFRPs as they adversely affect the performance and acceptance of eventually-machined composite parts. In this paper, a critical review has been conducted to offer a comprehensive understanding of drilling-associated damages for CFRPs by focusing on illustrating the damage formation mechanisms, classification, evaluation, and suppression. Recent advances addressing the damage issues in drilling CFRPs are also carefully reviewed by critically analyzing the scientific findings reported in the open literature. The fundamental effects of the fiber layup, process parameters, tool geometries/materials, cutting environments and process strategies on the formation and progression of composite damage are discussed. The article also outlines potential solutions and strategies to suppress the formation of drilling-induced damages for CFRP composites. Both researchers and manufacturers will benefit from this review article as they seek to achieve damage-free drilling of CFRP composites.

Glass fiber reinforced polymer (GFRP) composites are becoming more attractive in modern engineering fields due to their outstanding mechanical/physical properties. However, a thorough understanding of their drilling machinability is seriously lacking in the research community. The present work aims to address the drilling behavior of woven GFRP composites under varying cutting speeds and feed rates. Machining studies were conducted using two different diamond-coated special tools involving a double point angle drill and a dagger drill. The drilling machinability of GFRPs was comprehensively analyzed in terms of cutting forces, machining temperatures, drilling-induced damages, dimensional accuracy, and hole wall morphologies. Theoretical analyses and experimental characterizations of delamination damage were conducted for both special drills. A special attempt was made to clarify the impact of different drill shapes on the damage formation and extension of cut GFRP materials. The results obtained can supplement the expertise of composites machining and guide the damage-free drilling of GFRP laminates for academia and industry.

Ultrasonic elliptical vibration cutting (UEVC) is a promising technique to realize the crack-free machining of ceramic materials. However, the underlying crack suppression mechanism and its impact on the ductile-brittle transition (DBT) behavior of ceramics still remain poorly understood. In the current work, the material removal characteristics of 3Y-TZP ceramics under UEVC, including the crack propagation process, stress distribution condition, and critical transition depth, were rigorously studied by using both the smoothed particle hydrodynamics (SPH) simulation and the experimental method. It was found that the material removal behavior and critical transition depth were highly related to the ultrasonic speed ratio (Rs) that defines the ratio of the nominal cutting speed to the maximum ultrasonic velocity along the cutting direction. A critical (Rs) value of 0.128 was determined by the analytical method, beyond which the crack suppression mechanism of UEVC is mainly due to the time-varying cutting speed and angle. When the Rs is lower than the critical value, the reduction of the effective cutting thickness caused by the overlapping trajectory becomes a dominant factor in enlarging the ductile regime and in improving the machining quality of 3Y-TZP ceramics.

Magnesium alloys have been widely applied in the advanced fields of aerospace, medical implants, automobile, etc. However, the ignition risks of magnesium alloys, especially at high cutting temperatures, have to be considered in the machining process. This article conducts numerical investigations on the effects of cutting tools on the cutting behaviors, especially the cutting temperature of magnesium alloy AZ31B. The impacts of the rake angle, the tool edge radius, and the friction coefficient are studied by simulations based on the orthogonal cutting models using the DEFORM software. The simulation results are studied and compared to analyze the correlations between the cutting parameters and the cutting temperature, as well as the underlying mechanisms. The conclusions of this numerical analysis can provide specific guidance to the design of cutting tools for the magnesium alloys.